1. Field of the Invention
The present invention relates to a power converter, and more particularly to a power converter, such as a 2-level inverter etc., capable of performing the stabilized circuit operation by making the voltage in respective phases not affected by the voltage fluctuation resulting from the switching of the other phase switching devices.
2. Description of the Related Art
FIG. 3 is a circuit diagram showing the construction of an example of a conventional power converter (a 2-level inverter) that is generally used.
In FIG. 3, a DC power source Vd is connected between a DC positive bus P and a DC negative bus N. Further, a filter capacitor Cf is connected between DC positive bus P and DC negative bus N and in parallel with DC power source Vd.
On the other hand, between DC positive bus P and DC negative bus N, a U-phase first switching device Su1 and a U-phase second switching device Su2 are connected in series. Further, first and second freewheeling diodes Fu1 and Fu2 are respectively connected in antiparallel with first and second switching devices Su1 and Su2. In addition, a phase capacitor Csu of the U-phase is connected in parallel with a series circuit of first and second switching devices Su1 and Su2. A U-phase arm of the main body of the power converter (the inverter) is composed of these devices.
Further, between DC positive bus P and DC negative bus N, a V-phase first switching device Sv1 and a V-phase second switching device Sv2 are connected in series. Further, first and second freewheeling diodes Fv1 and Fv2 are respectively connected in antiparallel with first and second switching devices Sv1 and Sv2. In addition, a phase capacitor Csv of the V-phase is connected in parallel with a series circuit of first and second switching devices Sv1 and Sv2. A V-phase arm of the main body of the power converter (the inverter) is composed of these devices.
Further, between DC positive bus P and DC negative bus N, a W-phase first switching device Sw1 and a W-phase second switching device Sw2 are connected in series. Further, first and second freewheeling diodes Fw1 and Fw2 are respectively connected in antiparallel with first and second switching devices Sw1 and Sw2. In addition, a phase capacitor Csw of the W-phase is connected in parallel with a series circuit of first and second switching devices Sw1 and Sw2. A W-phase arm of the main body of the power converter (the inverter) is composed of these devices.
The output side of the main body of the power converter (inverter) is connected to a load such as a motor, etc. (not shown), which is controlled by the power converter at a variable speed.
Next, the assembly structure of the power converter shown in FIG. 3 is described below. FIG. 3A is a schematic plan view for explaining the assembly structure of the power converter shown in FIG. 3. In FIG. 3A, in the U-phase arm, a gate amplifier 11u (not shown in FIG. 3) is provided for generating gate signals to first and second switching devices Su1 and Su2. Furthermore, a cooler 12u (not shown in FIG. 3) is provided for cooling the heat generated by first and second switching devices Su1 and Su2.
Further in FIG. 3A, in the V-phase arm, a gate amplifier 11v (not shown in FIG. 3) is provided for generating gate signals to first and second switching devices Sv1 and Sv2. Furthermore, a cooler 12v (not shown in FIG. 3) is provided for cooling the heat generated by first and second switching devices Sv1 and Sv2.
Further in FIG. 3A, in the W-phase arm, a gate amplifier 11w (not shown in FIG. 3) is provided for generating gate signals to first and second switching devices Sw1 and Sw2. Furthermore, a cooler 12w (not shown in FIG. 3) is provided for cooling the heat generated by first and second switching devices Sw1 and Sw2.
As for the bus connection in the power converter, the U-phase arm is connected between DC positive bus P and DC negative bus N at a first position P3u adjacent to filter capacitor Cf. The V-phase arm is connected between DC positive bus P and DC negative bus N at a second position P3v a predetermined length lv distant from first position P3u. Further, the W-phase arm is connected between DC positive bus P and DC negative bus N at a third position P3w a predetermined length lw distant from second position P3v. 
However, such a conventional power converter has a problem shown below. This point will be explained referring to a detailed diagram shown in FIG. 4. FIG. 4 is a detailed diagram for explaining the problem of the conventional power converter shown in FIG. 3.
That is, in the assembly structure of the power converter shown in FIG. 3A, there are wiring inductances L1, L4 between filter capacitor Cf and the U-phase arm, wiring inductances L2, L5 between the U-phase arm and the V-phase arm, and wiring inductances L3, L6 between the V-phase arm and the W-phase arm as shown in FIG. 4.
Therefore, at the time of switching of respective phases, the resonance is taken place between these wiring inductances L2, L3, L5, L6 and phase capacitors Csu, Csv, Csw, and thereby the power converter becomes in extremely complicated operations. As a result, currents and voltages of the power converter fluctuate remarkably, and it becomes impossible to operate the power converter stably.
As a result, conventional power converters are only applicable to power converters of very small capacity.
As described above, conventional power converters have a problem that the voltage in each phase changes because it is affected by the voltage fluctuation resulting from the switching of other phase switching devices, and thereby a stable circuit operation of the power converter cannot be obtained.
Accordingly, one object of the present invention is to provide a power converter capable of performing the stabilized circuit operation by making the voltage in respective phases not affected by the voltage fluctuation resulting from the switching of the other phase switching devices.
These and other objects of this invention can be achieved by providing a power converter including a plurality of arms. Each of the arms is composed of series connected first and second switching devices, first and second freewheeling diodes respectively connected in antiparallel with the first and second switching devices, and a phase capacitor connected in parallel with a series circuit of the first and second switching devices. The power converter further includes a DC power source connected between a DC positive bus and a DC negative bus, and a filter capacitor connected between the DC positive bus and the DC negative bus and in parallel with the DC power source. Each of the arms of the power converter is connected individually to the filter capacitor between the DC positive bus and the DC negative bus.
In the power converter as described above, as each phase arm of the main body of the power converter is individually connected to the filter capacitor between the DC positive bus and the DC negative bus, the resonance is not taken place between the phase capacitor and the wiring inductances in each phase. Accordingly, no resonant waveform is applied to the filter capacitor. This is because generally the capacitance of the filter capacitor is 10-100 times as large as that of the phase capacitor.
Thus, as the phase voltage for each phase is separated, the stabilized circuit operation can be carried without affected by the voltage fluctuation resulting from the switching of the other phase switching devices.
According to one aspect of this invention, there is provided a power converter including a plurality of arms. Each of the arms is composed of series connected first and second switching devices, first and second freewheeling diodes respectively connected in antiparallel with the first and second switching devices, a phase capacitor connected in parallel with a series circuit of the first and second switching devices, and a filter capacitor connected in parallel with a series circuit of the first and second switching devices. The power converter further includes a DC power source connected between a DC positive bus and a DC negative bus. Each of the arms of the power converter is connected individually to the DC power source between the DC positive bus and the DC negative bus.
In the power converter as described above, as the filter capacitor in the power converter, filter capacitors are provided for each phase. The filter capacitor of each phase is included in the arm of each phase, and the arm is made as one unit. This unit is connected individually to the DC power source between DC positive bus and the DC negative bus to suppress the voltage fluctuation resulting from the switching of the other phase switching devices.
Thus, the stabilized circuit operation can be carried out by making the voltage in respective phases not affected by the voltage fluctuation resulting from the switching of the other phase switching devices.